1. Field of the invention
The present invention relates to a process for the preparation of a high dielectric thin film. More particularly, the present invention relates to a process for the preparation of a high dielectric thin film used to increase the capacitance of a condenser (i.e., a capacitor) in a semiconductor device.
2. Description of the Related Art
Remarkable progress has been made in the technologies required for accomplishing miniaturization of a semiconductor element having a high capacitance, high operation speed and high integration density and, accordingly, the development of a high dielectric thin film is now necessary.
Conventionally a sputtering method, a metal organic chemical vapor deposition (MOCVD) method, and a plasma chemical vapor deposition method are used as a means of preparing a tantalum oxide (Ta.sub.2 O.sub.5) film as the dielectric thin film of a condenser in a semiconductor element, but the characteristics of the Ta.sub.2 O.sub.5 film obtained by using these methods do not satisfy the necessary requirements.
Namely, a film obtained by the plasma CVD method has many oxygen vacancies therein, and these oxygen vacancies cause an occurrence of a leakage current. Also, the surface flatness of a film obtained by the MOCVD method is poor, in addition to the problem the oxygen vacancies. Furthermore, reproduction of the composition of the thin film obtained by sputtering is poor, due to a deterioration of the target, and further, the step coverage is poor.
To obtain a tantalum oxide thin film having good properties and able to be used for a capacitor in a memory cell, the following conditions must be satisfied: (1) good controllability of the composition of the film, (2) good fineness of the film, (3) good step coverage, and (4) good surface flatness of the film.
Accordingly, an attempt was made to employ an electron cyclotron resonance (ECR) plasma chemical vapor deposition (CVD) method.
This method, however, is usually employed at a low temperature, i.e., a temperature of lower than 300.degree. C., and this is why the ECR plasma CVD method is usually employed for depositing SiN, or SiO on aluminum.
The present inventors found that the tantalum oxide thin film obtained by the ECR plasma CVD method at a low temperature does not satisfy the four requirements mentioned above.
Therefore, the present inventors made various, diverse attempts to obtain a tantalum oxide thin film satisfying the above requirements, and surprisingly found that a tantalum oxide thin film satisfying the above requirements ca be obtained by the ECR plasma CVD method within a certain high temperature range, i.e., at a temperature of from 400.degree. to 850.degree. C.